Since the double-bed type ion-exchange apparatus for water treatment (hereinafter referred as double-bed) has been developed, its unique advantages have aroused wide concerns. During the application of such double-bed type apparatus, in order to obtain water having good quality after treatment, it is necessary to keep both the strong and weak resins in a state of proper separation, namely the strong and weak resin should possess an adequate difference of wet true density so that they can separate off from each other by hydraulic backwashing and sieving. It is generally required that the difference of wet true density of cation double-bed should be over 0.09 and that of anion double-bed should be in the range of 0.04-0.051. However, after the resins lose their efficacies, the separation of said two layers' resins becomes difficult because the difference of wet true density between them are two small. Especially for those double-bed comprised of anion exchange resin, such problems become more obvious. Therefore, the development and application of this technology are greatly restricte.
With the purpose of solving this technological problem of separating the two layers of ion exchange resins, two processes are disclosed in prior art. One is mechanical partition For example, Japanese Patent Application No. 62-284999 describes a two-chamber fixed double-bed type ion exchange resin apparatus and Japanese Patent Application No. 59-29902 discloses a floating double-bed type apparatus. Both the two apparatuses as described above use a partition disposed between the strong and weak resin layers which only allows liquid to permeate and does not allow the resins to pass therethrough to prevent the intermixing of strong and weak resins. Theoretically, such means can solve the above-mentioned problems, but in practical operation, a washing tower disposed out of the apparatus is needed for cleaning the resins periodically. Since the same system is jointly used for the two types of resins, if the resins are not completely transferred, or resins exist in the dead corner of pipes or in case of inadequate operation and malfunction occurring in intermediate water chamber (e.g. relaxing or breakage of the water valve bonnet), the phenomena of mutual ting between the two types of resins will inevitably arise. Besides, two types of resins in said fixed double-beds can not be effectively compacted, which leads to "layer confusion" during the counter-flowing regeneration and results in an unideal effects of regeneration. Whereas since there is no deep backwash during the regeneration in floating double-bed, thus the organics, suspensions and colloid silica trapped by the resins can not be removed during generation, which result in serious pollution of the resins, decrease of exchanging capacity, serious breakage of resins and no thorough regeneration in upper protecting layer, resulting in unideal results of regeneration, even unqualified regeneration and increase of acid-alkali consumption. In addition, the broken resins blocking in the water valve bonnet of the water chamber causes uneven distribution of water flow and increases the resistance to operation which are unfavorable for operation and regeneration. Furthermore, it is very difficult to clean the resins in the water valve bonnet, it needs an additional resin wiping equipment disposed out of the main body, resulting in further complicated structure of the apparatus, thus increasing equipment investments and space occupation and making regenerating operation more complicated.
Another regeneration process of fixed double-bed type ion exchange resin apparatus in the prior art uses a separation method of hydraulic sieving plus chemical conversion and hydraulic sieving. This method accomplishes effective separation utilizing the fact that the difference of wet true density between two types of resins after resin regeneration being increased But said method needs strong hydraulic backwash each time and needs further strong hydraulic backwash after the completion of regeneration. In this way, it not only increase self-consumption of water, but also makes operation complicated, and it is not favorable for realizing automatic control. In addition, this method also has the problem of "confusion layer" when counter-flowing regeneration method is used. Although co-flow method does not have the problem- of "confusion layer", it has low efficiency of regeneration, inferior water quality after treatment and high specific consumption of regeneration. Furthermore, said method needs larger space for backwashing, thus decreases the degree of space utilization for apparatus.